As piezoelectric material, well known is PZT (PbTiO3—PbZrO3)-based ceramics. PZT has excellent piezoelectric properties such as electromechanical coupling coefficient and piezoelectric constant; PZT is widely used in piezoelectric elements of a device such as a sensor, an ultrasonic motor, and a filter.
Incidentally, because of environmental demands, there is urgent need for lead-free products in recent years. Since PZT is used in industrial product, it goes without saying that it is necessary to replace PZT as piezoelectric material containing lead (Pb) with another piezoelectric material containing no lead.
Piezoelectric materials containing no lead (lead-free piezoelectric material) could include: barium titanate (BanTiO3)-based piezoelectric materials; alkali niobate-based piezoelectric materials such as compounds (KNN) having the general formula KxNa(1-x)NbO3 and compounds having the general formula (K1-aNaa)1-bLib(Nb1-c-dTacSbd)O3; and the like. It should be noted that piezoelectric material containing KNN as the main component (hereinafter referred to as KNN-based piezoelectric material) is described in [PTL 1] mentioned below. [PTL 1] discloses a piezoelectric material in which the value x of KNN is 0.02≦x≦0.5 and in which at least either of Fe2OO3 or Co2O3 is added to KNN. Common techniques of piezoelectric material are described in detail in [NPL 1] and [NPL 2] described below.